Peter Bodo has been covering tennis for over 35 years, mostly recently for ESPN. He is a former WTA Writer of the Year and the author of numerous books, including the classic "The Courts of Babylon" and the New York Times bestseller (with Pete Sampras), "A Champion's Mind."

Roger Federer went where no man has gone before on Sunday in Melbourne, joining Margaret Court, Serena Williams and Steffi Graf in the exclusive club consisting of players who won at least 20-Grand Slam singles titles.

Historic firsts are destined to be duplicated. Think of Babe Ruth's 700 home runs, Edmund Hillary's ascent of Mount Everest, swimmer Mark Spitz's seven gold medal Olympic performance. All have been equaled or eclipsed. But it's hard to imagine another man surpassing Federer. He earned this 20th at age 36 in his 19th year as a professional.

Only Aussie Ken Rosewall won a major at a later age, yet his career haul was just 12 majors, many of them earned before the game was opened to professional players in 1968.

Marin Cilic said it was tough to acclimatize to playing the Australian Open final under a closed roof against Roger Federer indoors after practicing outdoors earlier in the day when the temperature reached a high of 100 degrees.

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"All day I was thinking, 'How would I feel if I won it, how would I feel if I lost it?'" Federer said after the landmark win over No.6 seed Marin Cilic. "I'm so close, yet so far. I think I was going through the whole match like this. I've had these moments in the past, but maybe never as extreme as tonight. Getting to 20 is obviously very, very special, no doubt."

Federer's epic demonstration came at an excellent time for the ATP. Here was the beloved ambassador for the game, playing like a spry teenager as he shattered another men's record. But his feat utterly overshadowed a different story, one that may keep tennis administrators up at night in the coming days: The unexpected collapse of the group known as the Big Four.

It's almost certainly the end of an era, even if Federer's continued mastery mutes the fact.

This story is a darker one, because it's not like Rafael Nadal, Novak Djokovic, and Andy Murray, all of whom are over 30, are just running out of steam after enjoying great careers [you can include Stan Wawrinka in this group]. They're grappling with the perils of growing older in a punishing sport as they try to keep up with Federer. They've paid a high price, and it just may be that what they've really done is make The Mighty Fed look that much greater. If that's even possible.

Roger Federer became the second oldest men's player to win a Grand Slam and first to reach 20 titles. Clive Brunskill/Getty Images

This was the event at which the Big Four, the quartet that has ruled tennis for over a decade [with an assist from Wawrinka], was to re-form. Djokovic and Murray were returning from long layoffs due to injury, presumably to challenge No.1 Rafael Nadal and No. 2 Roger Federer. The two junior members were the ones who had elbowed aside their elders to rule from 2013 through 2016.

Both men left the tour with injury after absorbing quarterfinal beatings at Wimbledon last year. Neither 30-year-old is healed. Murray, the winner of three major singles titles and two Olympic gold medals in singles, is in worse shape. He had to resort to career-threatening hip surgery last month, when it became clear that rest and rehab simply weren't going to fix his hip.

Djokovic is a more complicated case. His three-year period of utter dominance came to a halt when he completed his career Grand Slam at the French Open in 2016. It was his 12th -- and most recent -- Grand Slam title. Troubled by lax motivation and private struggles, he hasn't been the same since. The elbow injury has further muddied the water.

Beaten by 21-year-old Korean sensation Hyeon Chung in the fourth round in Melbourne, Djokovic told the press: "I felt the level of pain was not that high that I need to stop the match. I wish I could have a little bit had more free points on the first serve, but I didn't. That's life. I have to move on."

The two main storylines in Melbourne intersected in the fate of Nadal, who was penciled in for a championship rematch with Federer. But yet another in the seemingly endless series of injuries that have plagued Nadal in recent years intervened, and he had to retire midway through the fourth set of a quality quarterfinal match with Cilic.

For the second straight year Roger Federer won the Australian Open after a five set final. XIN LI/Getty Images

"It is really tough to accept," Nadal said after he quit. "Especially after a tough December [Nadal had to forgo his usual preparations while still nursing a bad knee]."

Nadal's inner hip muscle injury isn't serious; he will only be out of action for about two weeks. But the recurring breakdowns are cause for concern in the 31-year-old's camp, as they interfere with his training and fitness regimen. The winner of 16 majors has missed eight Grand Slam events due to injury since he first appeared in one in 2003.

Just by being himself, Federer is turning up the pressure on everyone else. While players undoubtedly are performing better later in their careers, take Federer out of the equation and you see a lot of over-30 players struggling to hang on, but slipping. Recently that number included that pair of popular over-30 French stars, Jo-Wilfried Tsonga and Gael Monfils.

Federer is doing great despite the slow hard courts and strings that encourage endless rallies, but others, including some even younger players, are suffering. Milos Raonic and Kei Nishikori, both former Grand Slam finalists, are 27 and 28 respectively. They were MIA in Melbourne due to lingering injuries. Rising star Nick Kyrgios, currently No. 16, is just 22 but already showing signs of wear and tear.

"Somebody who is running the tour should think little bit about what's going on," Nadal said in Melbourne. "Too many people getting injured ... I don't know if they have to think a little bit about the health of the players. I don't know if we keep playing in this very, very hard surfaces what's going to happen in the future with our lives."

The statistics tell us that the last six majors were won by players over 30. It's easy to embrace that, and celebrate these "mature" athletes. But Federer accounted for half of those titles. Nadal [two] and Wawrinka [one at 30, one at 31] claimed the others, and one had to quit and the other barely started in Melbourne.

Federer makes it seem that the conventional wisdom about age and athletic achievement is a fiction. In having to keep up with him, his peers are demonstrating that it most certainly is not. Enjoy it while you can.